Apparatus for hydraulic brake systems



April 17, 1956 J. H. GEIGER 2,741,896,

APPARATUS RoR HYDRAULIC BRAKE SYSTEMS Filed May 221 1951 JNVENTOR.

JOHN H. GEIGER lATTORNEY I APPARATUS FoR HYDRAULIC BRAKE SYSTEMS s This invention relates generally to hydraulic brake sys- United States PatentQf tems and more particularly to a master cylinder and a v i mechanism for operating it.

According to conventional practice, passenger automobiles andlight or medium trucks are equipped with mechanical or hydraulic brake systems. Heavy 'trucks s are equippedY with air operated brake systems, but such systernsare not economically feasible for use in small or 'medium sized trucks. Mechanical brake systems have been found to be generally inadequate in medium sized trucks, principally because it is diiiicult and sometimes impossible for'the truck driver to apply suliicient pressure f to the brake pedal to obtain the braking power which is necessary to meet emergency conditions. Hydraulic brake systems which include the conventional type of master ,cylinder are also inadequate'inlmedium trucks for the same reason. In the prior art `hydraulic systems, A special master cylinders, comprising compound cylinder arrangements, have been devised for increasing the effective braking pressure as applied by the truck operator.

Such systems, however, are subject to the objection that they are exceedingly costly and, because of complex structure,osubject to certain faults such as leakage and other types'of failure which necessitate frequent repair and expense.

. i Stillanother object off this invention is to provide a novel brake pedal and connecting linkage for operating the master cylinder of a hydraulic brake system.

`A `still further'object of this invention is to provide a brake pedal and connecting linkage for operating ahydraulic cylinder having a mechanical advantage for multiplying the operating pressure applied by the truckV nature of a toggle joint or other linkages having high mev chanical advantage.

In accordance with this invention there 1s provided a mechanical brake operating linkage of the type which provides a certain mechanical yadvantage and has `a limited effective operating motion together witha hydraulic master cylinder which is adapted totake up the slack rin the brakes regardless of the degree of wear of the brake shoes and said limited motion. s

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. In the accompanying drawing:

Figure 1 of the drawing illustrates in cross section a preferred embodiment of this invention.

Patented Apr. 17,1956

ice

2 i Figure 2 of the drawing illustrates partially in cross seca ytion a second 'modification ofthis invention.`

Figure 3 of the drawingillustrates a third modification of `this invention.

Figure 4 of theA drawing isa cross sectiontaken on line 4-4 of Figurel'Z.l i i In accordanceiwith this invention,th`ere is provided 'a vmastercylinder-andv brake pedal operating Vmechanism comprising the master cylinder 101(Fgure l)abracket `11, a foot pedal operated lever 12, and an operating arm 13. Bracket 11 may be iixed to the master cylinder 10 by means of bolts 16 and 17, which screw into the master cylinder casting as illustrated in Figure-1 of the drawing. The foot pedal lever`12 may be pivoted at 4its lower. end of the bracket y11 by means of a suitable bolt 18 am chored to` the outer endof the bracket. Bolt 18 is intended to provide apivot point lying on an extension of thevlongitudinal axis of the` master cylinder. The operating arm 13 may Vbe pivotally mounted on the lever 12 by means of a bolt 19, mounted tor rotational movement in lever 12 in conventional fashion. Bolt 19 may be provided with athreaded bore 20 for adjustably receiving of arm 13. Thus, theportion 27 of lever 12 together with operating. arm 13 formsa toggle joint linkage betweenfthe pedal lever 12"and the piston23 which is movable into alignment with the longitudinal axis of master cylinder 10. Lever arm 13 is provided with a boot 28 which `is conventionally mounted over the end of cylinder 10 so that dirt and other debris may be prevented from entering the cylinder.` i l` s The -master cylinder. 10 comprises a casting which `is formed to provide a reservoir 30 having a filler plugl 31. Reservoir 30 may be connected with the master cylinder 24 by means of a` breather port 33, which permits ow of brake iluid between the reservoir and the cylinder 24 as the piston 23 moves forward and back, and a replenishing port 33a which connects thereservoir with the cylinder 24 when piston 23 is fully retracted.

"The mastercylinder casting kis also provided with a compensating cylinder 34, the purpose Yof which will be described subsequently. `This vcylinder includes a cap 35 which `is threaded at 36y to the master Scylinder casting. vWithin the` cylinder 34 there is provided a piston :38 and a cup leather l39, both of which are normally ymaintained in the position shown in Figurev l by means of a spring V40. The compensating cylinder isprovided with a port 42, which permits the flow .of brake uid between reservoir 30 and cylinder 34 whenever the piston -38 is moved upwardly or downwardly. There is also provided a p ort 43 and a port 45, both of which communicate with the cylinder 24 to permit the flow of brake fluid to and from cylinders 24 and34. 1 l `Piston '23 is provided Y with a first cup leather 47 for sealing the piston with respect to thek cylinder so thatforward movement of the piston creates pressure within the cylinder which maybe transmitted to an automotive hydraulic brake'system (not shown) through the "opening 48. The rear end of piston 23 includes a head portion 49 to which istitted acup leather or washerStl, which seals the rear end of the piston with respect to the cylinder to prevent the escape of brake i'luid from cylinder 24. For returning the piston 23'an`d thebrake-lever 3 a wshenSS, which may be retained in position by an 'expansion"ring"56"resting" within 'an' -annular sl`ot" in' 'accordance with conventionaly practice.

n From the foregoing description it will belapparent-that the forward movement otpistonl23 sJimit'ed because of the fact that "it reachests' -outermost' foriivar'rd` position Whenp'ortion' 27 of lever' Y12 and arm' 13 arein alignment with one another. Therefore, unless l special provisions are'ma'deg the maximum forward movement .ot piston 23 .will not move the brake shoes into `contact with" the brake drnrns' after'the" brake shoes. become Worn to a certain degree. To"the end thatl the `brake'shoes may be moved 'intog'contact witlrthe brake drums in spite of wear,".the master 'cylinder of 'thisinvention isv designed .togapply limited pressure 'to the brake system' during initial, move- "me'nt ofi thelever' 12..and .until portion" 27 .of lever 12 vis moved :to within. approximately V15 degrees of .alignment With the longitudinal. axis of master cylinder 10. Ports "43 and" 45 controLow of luid` during this initial .movement and are situated so'that cup lea-ther'47 will not coverthem until portion 27 is inthe 15 degree position. `Port 43 may be of larger fdiameter Athan port '4S whereby "therateoi" ow ofuid into cylinder 34 is decreased when `port"43'is closed by. cup leather`47. VVThis provides a 'cushion-like'effect on `the motion 'of the brake pedal. The 'piston 38 and spring 40 co-operate with. ports .43 and "45'to further control .the pressure in .cylinderf 24. since l spring 4t) is designed, in etect, to create a back pressure .incylinder 24 sufficient to insure `that the brakeshoes will 'have contacted' theldrums when cupI leather.f47f..nally 'covers port 45.

` The modification ofthis invention which has been '.de- 'scribed in Figure 1' of the drawings operates. asfollows. vWhen the brake 'lever 12`is depressed,` its initial movement' does not multiply except to a limited extent the `.pressure which is impressed by the operators foot on the "brake pedal; but as the lever travelsv.to...the right, the "mechanical advantage of arm 27f.and.the. operating arm "13increases asthe angle increases between. arm'..13 and the portion27 of the lever 12. Piston 23 moves foivvard under pressure of. arm 13 and brake lfluid llowslhrough opening 48 intothe brakesystem forinitiallytaking up 'the slack between the brakeshoes and the brakefdrums. .The initial movement of piston 23 creates arelativelylarge llow Tof oil at a relatively low pressure by reason vof .the factthat .brake fluid is permitted to -ilowv` through. the auxiliary port 43 and the compensating cylinder .port 45 until arm. 27 reaches its 15 degree position as explained previously. During'this intiahmovement ot .piston 23, only enough pressure is createdtq Apick .11p...the.sla`ck...in the brakeshoes, 'after which the pressure .necessarily-increases within themaster. cylinder .scientlyto overcome the pressure exerted `byfspring` 40, whereby piston v38 and cup leather 39 move upwardly. .-.At. this. point oil is permitted to' ow through the port` 42 into thereservoir 30`whereby only limited back .pressure iscreated within the cylinder 34. Piston 23 eventuallyclosesthenport-43 'atwhich timefflowbf brake lluid is .restricted to .the port 45 so that there is a marked .decrease in Yrate of. flow and a corresponding increase ,in pressurewithimthemaster cylinder. Thus, the, pressure.increasesonfthe brake .,shoesto initiate .ellec'tiveapplicationof theebrakes. f-Pis-Y ton 23 .continues to moveorward .until port 4Szis closed, at whichtirne the pressure withinthemaster,cylinderand within' the brake system increasesy at a .veryzliigh Tate. .#At this. time the arm. 13 and the arm- 27 are. at arelatively large angleto one .another whereby.theimeehanical-advantage .of the .toggle joint'Y becomesY veryfgreat. so -that pressure .on the foot .pedaL ismultiplied as muchsas twenty- ...brakes by:reasonf.ofthefact'that theipiston haszprogressed beycindpmt 45 to theipointwhereuli pressuresis exerted .onnthe brakesystem. .Thus-.the ports AandMSapei-mit apanage take up the slack in the brakes at some time during the ""initiabmovement ofthe brake pedaland'regardless of the amount of wear on the brake shoes. Then, at the time that the mechanical linkage consisting of arms 13 and 27 is at a position where the mechanical advantage is approaching a maximum, the brake shoes are always applied to the brake drums despite varying degrees of wear.

*Y Az-diierent .modification of- 1 the inventionr-is disclosed in Figure 2 and like reference characters'are4 utilized Vfor designating parts corresponding'toth'osevof Figure l. Insteady of. thetoggle joint betweenthe.. brake pedal .and the piston `v'of the master cylinder there is providedY a cam 60 having a cam=surface'tofflsuchxcnrvature that increased mechanical advantage is obtained when the brake pedal approaches the limit of its operational movement. A cam follower 63 co-operates with the cam surface 61 and is mounted on the .end of an operating arm.64. by meansv of the'follower;'riiouriting'6f Arm'l4l may be thread'edinto mounting '65 and locked withlrespect thereto by lock nut 66. For guiding'arm' 64"there` is provided an apertured strut 67 extending" b etween.the side.' walls of' bracket'-l. "For preventing .access of'foreign 'matter .tomaster cylinder '10there is provided a boot' 68 which may include an aperture. (nlot"shown)for accommodat- Vifngstrut' 67 and be conventionally mounted between'the `eidl 69 'of "master cylinder '10. andthe.mounti ng 'mem- "ber 65. v

In this Vmodification of the invention"there..is pro- 'videda pvoppet valve'in'ste'ad of a cornpensating'c'yliiider "for controlling the flow of brake"iluidduringithdtime Ithat`thefbrake shoes are' being ."tak'en' up. The 'poppet vval'veconsis'ts of a ball'70,'seated in a port 71', and"main tained inlposition by 'means`.of a spring`73which is in iturn'ih'eld'injpositionqbyrneans of an adjustable :screw '.75 mounted in a 'plug"76. threaded to the reservoir. ""By rotatifngl the 'screw 7.5.' 'the' tension on' Yspring'f '73. 'may' 4be adjusted to, in turn', adjust'the pressure Whichis' required 'to'unseat'ithefball70. ."Port 71 'correspondswithf port 40 '2255 'ofFigurel and accomplishesthe-same'purpose.

`Asiri' the'caseo'the lirst mo'dication of this' invention, when pressure is initially 'applied "to "the" fot'ot pedal,` fthe cam 61.moves operating arm 64 and .therewith pis'tori"23 vforward within the cylinder 24. The. pressure increases within the cylinder 24'" taki'ng up'thefsiack.of'the'brake .shoes as .in the modification described in Figure 1. This pressure is determinedbyfthefstrengthand adjustment of spring 73 'ort"the.poppet valve '70.' This springs'ho'uld be adjusted vto crea'te'jorily sfcient pressure'td 'takeup the slack between the brake shoes andtthe'brakeidriim.

. Port 71 l is situated so i.' that "fthe Vcup"fle'ther VA"47 covers .the"port'T/lafterapproximately:25 degress of movement of cam 60, atv whichv time maximum pressure .s` `createdffbyY reason orthe *fact L'thatl` theu'id 'can no longer`- flow into'the 'reservoirtland' also 'by reason'of the .fact that .the .lever l2. has moved the carn surface 61' Lto." 'the point` "where it: provides 'l the A'irra'xi'murnrne- .The modification illustrated ..in Figure' 3ofthedrawj n'gs' issirnilar'to that illustrated itr'F-igure"2,f'except^that Vprovisions. are made for preventing'fracture 'of the cup VAleather. This `modification.may 'include either-of me- "chani'cal 'linkagesofFigure 1 ora-2. It has been *found bY-experiment"that"pressure"'within the` cylindersome- "timesises'to'such a-point thatfwhenthe Icup'leather is opposite the equalizing port"71,"fo1' example,"theI pressure'is scient to 'fracture .the cup leather and allow 70 leak/age. Accorditiglyg inlthe `modiiication oifgurc 3 .fofthef.drawingslthelequaliziiig port 71.is situated so the cup' leather' 47 moves beyond equalizmg .port '.71fdripg the initial and W pressurepartof the..st'roke.-.ofrthe .piston. There is provided. acompen'sating cylinder; smi- 75 lar in some respects-to thatfslnowmin Eigure Abithe drawings having a port 80 which is beyond the outerA ex tremity of the stroke of piston 23. The compensating cylinder differs from that shown in Figure 1 in that there is provided a stop 81 which is threaded to the cap 35 and can be adjusted and locked by means of thelock nut 82. During initial forward movement of piston 23 pressure is created as` described in connection with Figure 2, and after port 71 is covered and the slack ofthe brakesv is taken up, piston 38 and cup leather 39move upwardly as the pressure in cylinder 24 increases until suchtime as piston 38 engages with the stop 81. Oil can no longer flow through port 80 and therefore maximum pressure is applied to the brake shoes, This occurs, at the time that the toggle linkage or thecam is providing the maximum mechanical advantage.A i i Fromthe foregoing description it is apparent that there is provided in accordance with this invention a simple brake operating mechanism having high mechanical advantage with simple and` economical structure. Clt should be further noted that this mechanism always applies the brakes after the same angle of movement of the pedal. Even though this is true, the slack is always taken up in the brake shoes before the pedal reaches its brake application angle of movement.

`While this invention has been disclosed as includingy certainV forms of elements which make up the complete assembly, it should be clearly understood that other forms Aof elements may be substituted by those skilled in the art. `For example, there are other forms of mechanical linkages which may provide sufficient mechanical advantage in accordance with the inventive concept. Other forms of'pistons, cup leathers, poppetvalves and compensating cylindersr will also be obvious to those skilled in the art.

While there has been described what is at present cona sidered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the apt pended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.`

I claim: v Y a l. Brake control apparatus for hydraulic brake systems comprising a master cylinder, a piston therein, pedal operating means connected to said piston comprising a pedal lever and a pressure arm connected to said piston to form va knee of a toggle joint whereby movement of said'pedal lever moves said lever and arm into a straight line relationship and therewith said piston from a retracted position to a forward position, said master cylinder comprising a l compensating cylinder having'a compensating port, means for controlling llow in said port and `providing a limited,

brake operating pressure zone during initial advanceof said piston, said piston being movable beyondisaid port to stop ow of uid therethrough and to create maximum brake operating pressure. i

v2. Brake control apparatus for hydraulic .brake `systems comprising a master cylinder, a piston therein, pedal operating means connected to said piston comprising ay pedal lever pivoted at one end ,thereof and a pressure arm con-4 nected between said lever and said piston at an' obtuse Yangle to said lever to form a knee of a toggle joint whereby movement of said pedal lever moves said lever Yand arm into astraight line relationship and therewith said piston from a retracted position to a forward position, said master cylinder comprising a reservoir, a spring biased valve connecting said reservoir and said cylinder for providing a limited, brake operating pressure zone during initial advance of said piston, and a compensating cylinder connected to said master cylinder beyond the most forward position of said piston and comprising a chamber of limited capacity for permitting limited displacement of .fluid from said master cylinder, thereby to create maximum brake operating pressure after said chamber4 is `filled.

j 3. Brake control apparatus for hydraulic brake systems comprising a master cylinder,` aA piston therein,- pedal operi ating means connected to said piston comprising a pedal lever pivoted at one end thereof and a pressure arm connected between said., lever and said piston atfan obtuse angle to said lever to form a knee of a toggle joint whereby movement ofvsaid pedal lever moves said lever and arm ,I into a straight line relationship and therewith' said piston vfrom -a retracted position to a forward position, said master cylinder comprising a reservoir, a valve between said `reservoir and said'cylindcrfor providing a limited, brake operatingpressure zoneV during advance of said piston, and; a compensatingv cylinder connected to said master cylinder beyond themostforward position ofsaid piston and comprising a piston in said compensating cylinder,

for creating greater brake operating'pressurm and an adjustable means in the path of said compensatingcylinder piston for limiting the Imovement thereof to create maximum brakefoperating pressure. Y

4 4. Brake control `apparatus for hydraulic brake systems comprising a master cylinder, a piston therein, pedal opv eratingmeansxconnected to said piston comprising a pedal lever pivoted at one end thereof and a pressure arm connected between said lever and said piston at an obtuse angle to said lever to form a knee of a toggle joint whereby movement of said pedal lever moves saidlever and arm intoy a straight'line :relationship and therewith said piston from aretracted position tota forward position, said master cylinder comprising a reservoir, a 'replenishing port connectingsaid cylinder and said reservoir slightly in advance` of the retractedposition of said piston, a spring biased valve in advance of said replenishing'port for providing a limited, brake operating pressure zone during advancevof said piston'beyond said replenishing port, and a compensating cylinder connected to said master cylinder VV-beyond the most forward position of said piston and com- ,-prising a piston in l said compensating cylinder, a com angle to said lever to form a knee of a toggle jointwhereby movement of said pedal lever moves said lever and arm into a straightline relationship and therewith said piston from a retracted position to a forward position, said master cylinder comprising a reservoir, a replenishing port connecting said cylinder and said reservoir slightly in advance 'of the retracted position of said piston, an equalizing port `in advanceof said replenishing port, a spring biased valve for controlling flow` in said equalizing port and providing a limited, brake operating pressure zone during advance of said piston between said replenishing and equalizing ports, and a compensating cylinder connected to said master cylinder beyond the most forward position of said piston and comprising a spring biased piston in said cornl pensating cylinder, a compensating cylinder port for connectingsaid master cylinder and said compensating cylinder for creating greater brake operating pressure and an adjustable stop in the path of said spring biased piston for limiting the movement thereof to create maximum brake operating pressure. y I

6. Brake controlapparatus for hydraulic brake systems 'comprising a master cylinder, a piston therein, pedal operating means connected to said piston comprising a mechanical linkage having a mechanical advantage which increases from a minimum in a retracted position to a maximum at an advanced. position, said'master cylinder comprising a reservoir, and means for controlling ow of fluid fromv said cylinder to said reservoir and providing saigner-,ace

E17 -aflimitedgbrakeoperating-pressure'fzoneand brake operating pressure zonet duringZV1 advance 'ofsaid -piston. n f

` 7.="^Brake -control apparatus for-hydraulic brake systems comprising almaster cylinder, apiston-therein; pedalop Y erating: mea-ns connectedl tosaidj piston comprisingaimechanical Vlinkage having a; mechanical `advantage 1 tand* a limited stroke at'fthe''endof whichf maximumI mechanical -Ladvantage-occurs,v saidmaster cylinder comprising a Areserelvoir, an equalizing-port connecting said cylinder and-said reservoir-'in advancey of the retracted position of saidpisl' tom-tandl meansfor-controllingow in said port and-pro :'viding-y a limited, -brake operating Lpressure zone during advance of said-piston --betweenthe retracted position of .said pistonand equalizing-port 8.- r`Brake control--appar-atus'for hydraulic Abra-ke systems -comprising a master cylinder; -aA piston thereiny pedaloperating means connected-to-said-piston comprising a-pedal #levert andpressurev arm connected to formAvv a knee of a togglejointwherebymovement-of said pedal :lever moves 1 said lever and arrn 'fintoa fstraight': line relationship and therewith said f piston from `a1retractedposition to a' forwardV position;- said l`rnaster cylinder comprisingl a reservoir, anequalizing port connecting-said cylinder and said reservoir in adv-ance ofthe retracted position of 'said piston,- andl means for controlling-110W :in Isaid-portand pro- '-.viding` a limited,A brake-'operating pressure zone t during f advance f ofsaid npistr'Jn`^'-betw`een the retracted i position e 'of said piston Vandfsaid equalizing-port.

19.- Brake `control apparatusffor-hydraulic'- brakeesystems `comprising a master-cylinder; afpiston therein,-pedal operating means conneetedfto :said piston* comprising a f-pedalflever pivotediat one endithereofand a pressure arm connected between said-'levenaudlsad piston at- -an obtuse 'tangle to--said.. leverf'toforma a-'fknee of-r a toggle-'joint wherebyy movement of rsaid pedallever =moves V'said -lever andf armi-into a` stra-ight line-relationship and therewith said piston from a retracted-positionfto a forward position, fsaidmaster-cylinderl comprising a reservoir; anequaliz- -ing -port connecting: s'aid'tcyliriderfand' said :reservoir-in aadvance of -the lretraeted-positionlof -sa`id-pistonf-and a valve for controlling flow in said port and providing-.a 'limited; brakeoperating pressure--z'one'- dur-ingfadv-ance of `saidpistonbetweenthe retracted-position ofsaidfpiston and saidequalizing port.

- `V10.`IBrake Y-control-jappar-atus for hydraulicv brake sys- 4vtems comprising am-aster'cylinder', apistonfthereinypedal `.operating means 'connected toffsaidpiston ivcornprisinga -pedal lever pivotediat one'endfthereofand a-pressure' arm connected YbetweenV sa'id lever and -said f piston-iat anobtuse angle-to saicldever` tolform a-imee of a -togglejoint whereby :movement-"ofI said [')edal'leverrnlovesl said lever -andarm into: a* straighti line 'relationshipand l"therewith saidy piston :from ametractedjpositionto a'forward--position, said 4master cylinder-'comprising a-reserv` ir,5v a 'rel plenishingl port-`coiineetingrsaid"cylinder :and sa-id' reservoir slightly in 4advance the-retracted' 'positiony `of said v piston; Yan equalizinglportirr"advance of* said 'replenishing port, Aandl a `spring*biased"valve'forcontrolling ilow -in "said port vandproviding a limitech---brake'operatingpressure zone-f during `advance of saidpiston* between' saidy vcompensating "and-equfaliz-ir1g`poi'ts.

llfBra'ke controllapparatusfifor hydraulicbrakef'systems 4corriprising a'mast'eiicylinder, apiston' therein;A pedal.

- operating means cor'mezteditci saidelpistoncon'lprisingY a linkage having' aemechanical :advantagewhich increases from a minimum in a retracted' positie-nto' a' maximum at an ladvancedpositionsaithmaster cylinder comprising t vot" :saidw tpistonfrfon v'providingi `airlimited;,-brake operating pressure. zoney `dtiring'advance:of-'said piston between-said t :compensating cylinder. and'said firetfracted position.

:12Tl Brakeucontr-olfl apparatus sfor-liydrauliclbra'ke:sys-

tems :comprising i a- :master 1c`yl=irider,r,` aI pistonH therein,

pedal-foperatingfmeans connected to isaid-piston compris- :fingfa'ftoggle`v joint wherebyimovement of saidpedal =lever ffrr'ioves-fsaid leverand arm into aA straight line yrelationship v andftherewith Ysaid-piston from a retracted position lto a *forward'Iposition,sa'idzmaster cylinder-having a compen- -sating Vlcylinderfconnected thereto adjacent the most-forward position of .said piston for providing alimited, brake f operating pressure-zone lduring Aadvance of said piston *between said compensating cylinder and A'said retracted positon.

1: 13. Brake control'l apparatus for -hydraulic brake. sys- -te'msreomprising-almastercylinder; a piston therein; pedal iopera'tingr--means `connected toV -saidpistonA comprising a Lperlal-lever-pivr=ted-atone end=thereof anda pressure `varm connected between said lever and said-piston at--an obtuse `v-I'anfgle"tofsaid-lever tri-'formA ay knee of a'togg'le-'jointf-where- A{by -movement =of saidpedal levermoves said l-leverx and larrn-in'to' a A-straight li-ne relationship and ytherewithfsaid Apiston ifrom a-fretrac'tedposition -to-awforward position, Vsa'iderria''ster' cylindetfhaving a compensating cylinder con- `4nected'ftliereto'adjacent the :most forward position of -s'aid-v piston for providing a limited, brake-operatingpres- 'sure zoneduring-advance^of-said-piston between said compensating cylinder and said` retracted position Vtand :comprising a `slgiring'biased pistonf-insaid compensating cylinder, and a compensatingcylinder port for connect- Iing-said masterc-ylinder and -said compensating cylinder for icreatirig-A limited brake operating pressure,

I"idf-"tirelire control apparatus forhydraulic brake -sys` 'items comprising a master cylinder, a-pis'tontherein, pedal operated `-`means connected --to said piston rto provide-increased rnechanical' advantage vwith* increased angular *movement'vof-said pedal 'neans ande-means adjacentthe most forward position of said piston for providing a li-mitedbrake loperating pressure zoner during initial advancefofsaid `pistolrandthereafter for providing a 4higher brakeoperating'pressurezone locatedY forwardly of the -lirited'pressure `zone.

15;' Brakecontrolapparatus for hydraulic brake A'sys- `v-tems-corriprisingafmastercylinder; a piston' therein, pedal operating l@means connected to said piston comprising a cam mechanism connected to said piston, said camV having t ars'urA-facer" designedv toxprovide increasedmechanical advantage'withincreased angular movement, and means for providing' a-1imit`edg1brake operatingV pressure zoneA dur- `ing` initialA advance of 'said piston 'andthereafter' for providing a' higherbrake `operating pressure zone located `forwardly; of' the f limited pressure zone.

*^'1;6.' Brake control apparatus forbydraulic br-ake sys- Ltems -'comprisingav master cylinder,Y a piston therein, lp'e'dal operating means connected tosaid piston comprisfing' alnklageidesigned to provide increased mechanical ^`advantage with'fincreased angular movement thereof, and "-nieaiisjassociat'ed' with said cylinder for providing a -li1nited,brake 'operating pressure zone iduring initial advance `of said piston and thereafter for providing a v`'higher brake operating pressure-zone located' forwardly f of'the limited pressure zone.

17." Brake` jcontrol apparatus Vfor hydraulic brake sys- .'tnis comprising aamaster cylinder, apiston therein, `.pedal.ppcratingmeans connected to ,said piston .comprislingaypedallever; anda pressure arm :connected iQ Said ,-.pistontorforrn a kneeof a toggle joint whereby movement of- 1said-lpedalvfleverymoves l:said-flever and arminto' a .-.Lstiaightulinei relationship and: therewith` ysaid; pistons from a attretractedYA position to a forwardzposition, s aidvmaster -cylinider vhavingna-reservoir in combination` .therewith :which-containsV uidmnder atmosphericpressure, l means @operativeto sevensaid-y corun'iunicationjupon'v -first protraci 'tilelftovementiofffsaid-piston; equalizing--rneans effective '-Tafter'ethe-z'rffiresaidi first piston `moverri'ent for providinga -limited?brakefoperatingpressure rzone`v during Ysubsequent pistonladvanceme'nt; and-meansfordisabling-said equaliz- 5 ing'mcansf'upofurther advance-fpistonmovement' whereby maximum brake operating pressure is created near the limit of the pistons protractile stroke.

References Cited in the le of this patent UNITED STATES PATENTS Heidloi Sept. 7, 1937 10 Kerr Feb. 22, 1938 Weihe May 2, 1939 Staude Aug. 8, 1939 Godsey, Jr Sept. 21, 1943 Roy Mar. 30, 1948 Roy Aug. 15, 1950 FOREIGN PATENTS France Mar. 25, 1935 Great Britain Nov. 18, 1938 Italy lune 27, 1933 

